The challenge takes the form of a question that the Supreme Court has crafted itself from six petitions by state and industry groups, and to make sense of it one has to jump back a few years. In 2007, the Massachusetts v. Environmental Protection Agency case ruled that the EPA could limit greenhouse gas emissions from new motor vehicles if they posed a threat to public health. This “threat to public health,” is key, as it puts carbon emissions under the EPA’s purview as a pollutant that can be regulated under the Clean Air Act.

Two years later the EPA proposed limits regarding not only new moving vehicles, but stationary emitters such as power plants, and since 2011 these big stationary emitters have been required to apply for permits from the EPA to construct new facilities. In order to be approved for such permits, companies “may have to use pollution controls or otherwise reduce greenhouse gases from their operations,” according to NPR.

But now the Supreme Court will examine whether the EPA “permissibly determined that its regulation of greenhouse gas emissions from new motor vehicles triggered permitting requirements under the Clean Air Act for stationary sources that emit greenhouses gases.” Or, in other words, whether they went beyond the reach of the Clean Air Act in regulating emissions from power plants. What’s important—and undoubtedly good news—is that the Supreme Court declined to hear challenges as to whether or not the EPA has the right to regulate greenhouse gases; rather it is a matter of how they regulate them.

In a surprise to no one, the groups that introduced the challenge to the EPA legislation appear to be largely concerned with the cost of regulating emissions. In a petition to the Supreme Court, trade groups claimed that limiting “greenhouse gas emissions from stationary sources represents the most sweeping expansion of E.P.A.’s authority in the agency’s history, extending its reach to potentially millions of industrial, commercial, and residential facilities across the country, at costs estimated to run into the tens of billions of dollars per year.” (via New York Times)

According to the Guardian, oral arguments are expected to be heard in early 2014 with a ruling to be issued by the end of June.